player made terrain is a gamechanging skill that belongs in a champion's kit that can be balanced around it. Also, riot dislikes super specific hard counters, which is why they took out sword of the divine. An item that was made specifically to counter jax was bad design, so they just remade jax.

We have anivia wall and trundle's pillar, I dont see how this is gamebreaking with cooldown and a reasonable size

Because the whole reason anivia and trundle are good are BECAUSE they have terrain. If terrain was given to anybody, blinks would become even more dominant and those two would most likely drop off the face of the earth. Its not game breaking, just extremely game changing for no reason.

We have anivia wall and trundle's pillar, I dont see how this is gamebreaking with cooldown and a reasonable size

1.) They are a part of a champions kit. Just because something that is balanced for one person on a team to have does not mean its fine for five people on a team to have(Stealth is fine on eve/twitch/shaco. If you made an invisibility pot, it would be stupidly imbalanced)

2.) Your suggested duration is 25 seconds , which is about four times longer than either pillar or wall. For 100 gold you can now trap the entire enemy team in your jungle for the duration of an entire team fight...no